The present invention relates to a positive-working photosensitive composition comprising a photosensitive compound, a binder that is insoluble in water and soluble or swellable in an aqueous-alkaline solution, and a dye.
Photosensitive compositions containing a novolak or a polyvinyl phenol as the binder and, for example, an o-quinone diazide as the photosensitive compound have been in use for a long time for the preparation of high-resolution patterns in the fabrication of semiconductor devices. Because of the increasing miniaturization of functional elements, increasingly high demands are placed on the optical resolution of these photosensitive compositions. In particular, difficulties are expected when patterning is effected in the vicinity of the limit of resolution of the optical exposure systems. In these critical areas, resolution is, above all, influenced by disturbing optical effects, such as interference phenomena and undesirable reflections of scattered light from the substrate surface. Effects of this kind can partly be avoided by increasing the non-bleachable absorption of the photosensitive compositions. For this purpose, for example, substances that absorb light in the actinic region are added to the photosensitive compositions.
It has been known for some time to add absorbing substances to photosensitive compositions. As described in EP-A 0 026 088, for example, the image pattern produced can be improved by adding dyes to negative-working photoresists.
The addition of dyes to positive-working photoresists has been described for the first time by A. R. Neureuther and F. H. Dill ("Photoresist Modeling and Device Fabrication Applications", in Proceedings of Symposium on Optical and Acoustical Micro-Electronics, Polytechnic Institute of New York, Apr. 16 to 18, 1974, pages 223-249). According to this publication, the dye addition reduces the adverse influences of interference effects on the optical resolution.
According to the paper "Submicron Optical Lithography: I-line Lens and Photoresist Technology" [SPIE Proceedings, Vol. 470, pages 22-23 (1984)] by H. L. Stover, M. Nagler, I. I. Bol and V. Miller, optical resolution is markedly improved by the addition of an absorbing dye which absorbs light in the region of the exposure wavelength of .lambda.=436 nm. However, the exposure time required to generate image patterns has to be considerably extended, compared with a system that does not contain this absorbing substance.
PCT WO 86/01914 describes a process in which the production of photoresist patterns is also improved by the use of a non-bleachable, light-absorbing additive. In this reference it is also pointed out that the exposure time has to be extended by about 50 to 150%, compared with a photoresist without absorbing substance. Particularly preferred dyes mentioned comprise coumarin derivatives.
A coumarin derivative is also described by I. I. Bol in "High-Resolution Optical Lithography Using Dyed Single-Layer Resist" (Proceedings Kodak Microelectronics Seminar 1984, pages 19-22) and the significant improvement of the photolithographic properties of a photoresist is confirmed.
The influence of substances absorbing light in the actinic region on the photolithographic properties of positive-working photoresists is described in detail by A. V. Brown and W. H. Arnold in "Optimization of Resist Optical Density for High Resolution Lithography on Reflective Surfaces" [SPIE Proceedings, Vol. 539, pages 259-266 (1985)] and by M. P. C. Watts, D. DeBruin and W. H. Arnold in "The Reduction of Reflective Notching Using Dyed Resists" (Proceedings of Seventh International Technical Conference on Photopolymers, Ellenville, N.Y., October 1985, pages 285-296). According to these references, the solubility of the photoresist compositions in the aqueous-alkaline developers used is reduced by the addition of substances absorbing light in the actinic region. As a consequence, the photosensitivity of these photoresists is reduced considerably.
In their paper "Improving Linewidth Control over Reflective Surfaces Using Heavily Dyed Resists" [Journal of the Electrochemical Society, Vol. 133, No. 1, pages 192-196 (1986)], T. R. Pampalone and K. A. Kuyan describe the influence of high concentrations of absorbing substances in a photoresist. According to the reference particularly good results are obtained with photoresists having a very high absorption in the actinic region. Also in this case it is found that the absorbing compound added clearly reduces photosensitivity, e.g., by a factor of 5 or even more.
U.S. Pat. No. 4,575,480 also describes photoresist formulations containing substances that absorb light in the actinic region. The compounds mentioned are distinguished by their low tendency to sublimation and their high absorption in the actinic region. It is a disadvantage of these photoresist formulations that--depending on the concentration of the substance added--they have a markedly reduced photosensitivity.
Similarly, Japanese Patent Applications 86-159626/25, 86-165777/26, 86-174465/27 and 86-174466/27 describe photoresist formulations that contain absorbing substances that are non-bleachable and do not sublime. In all cases, however, the exposed portions of the resists have a noticeably reduced solubility in the developer solutions.
Photoresists that, apart from a dye absorbing light in the actinic region, also contain a component that increases their solubility, in particular a trihydroxybenzophenone, are described in U.S. Pat. No. 4,626,492. The trihydroxybenzophenone is added in quantities ranging from 12.8 to 13.1% by weight, which, however, leads to a considerable deterioration of the thermal stability of the photoresist. Moreover, a decline in the processing latitude of the resist is observed, since the developing rate strongly depends on the prebaking temperature of the resist film.